<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        #test1 {
            box-sizing: border-box;
        }

        .c500 {
            margin-right: 10px;
            display: inline-block;
            border: 1px solid;
            width: 500px;
            height: 500px;;
        }

        .test-display {
            width: 500px;
            height: 500px;
            border: 1px solid #00b3ee;
        }


    </style>
</head>
<body>
<div id="test1" class="c500">
    1
</div>
<div id="test2" class="c500">
    2
</div>

<div class="test-display"></div>

</body>
</html>